An image decoding method according to the present document comprises the steps of: deriving flag information indicating whether valid coefficients are present in a second area excluding a first area of the upper left corner of the current block; parsing an MTS index from a bitstream on the basis of the flag information indicating the absence of valid coefficients in the second area; and deriving residual samples for the current block by applying a conversion kernel derived on the basis of the MTS index to conversion coefficients of the first area, wherein the flag information may be derived by determining, for each scan sub-block in which the valid coefficients are scanned, whether the valid coefficients are present in the second area.
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2. The image decoding method of claim 1, wherein the MTS index is inferred to 0 when the MTS index is not parsed.
5. The image decoding method of claim 4, wherein the scan subblock is scanned according to the reverse diagonal scan order from a last scan subblock including a last significant coefficient in the current block.
7. The image encoding method of claim 6, wherein the MTS index is inferred to 0 when the MTS index is not encoded.
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November 9, 2020
April 16, 2024
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